1. Field of the Invention
The present invention relates to a fuel cutoff valve that is mounted on an upper wall of a fuel tank, and opens and closes a connection conduit to connect the fuel tank and outside.
2. Description of the Related Art
The upper part of a fuel tank is typically equipped with a full tank regulator valve connected to a canister, discovered in Japanese Patent No. 30648924, or with a fuel cutoff valve (rollover valve). The valves, by opening and closing at a prescribed fuel level, ensures venting of the fuel tank to the outside, as well as preventing fuel from flowing to the outside. A rollover valve is designed to shutoff fuel to the outside at a fuel level above the full tank level in order to ensure venting when the vehicle leans or slaloms during driving.
In line with increasing diversity of vehicle types and larger cabin space in recent years, the issue of making fuel tanks flatter has become a topic of interest. However, fuel cutoff valves adapted for use in flat tanks must meet the following conditions. Specifically, in order to reduce the proportion of dead space in the upper part of the fuel tank, it is desirable for the fuel level at which valve closes (valve closing level) to be as high as possible. Also, when the fuel in the fuel tank surges during sudden turning of the vehicle or the like, since in the case of such a sudden rise in fuel level the float will fail to rapidly keep pace with the fuel level, if the valve closure level is high for the reason mentioned previously, fuel will tend to flow to the outside of the fuel tank (into the canister); it is necessary to prevent such outflow of fuel. Where the height of the float has been reduced to afford a shorter fuel cutoff valve adapted for a flatter fuel tank, since the float tends to bob up due to rising vapor produced when a large volume of fuel vapors within the fuel tank flows into the canister, it will be necessary to design the float to resist ascension caused by the rising vapor so as to prevent closure of the fuel tank.